What is an excess reactant?
An excess reagent is one that is present in large enough quantities that it does not restrict the outcome of the reaction.
The reactant that doesn't fully react
In a stoichiometric set-up, in reference to either a synthesis or combustion chemical reaction, there are two reactants: The limiting reactant, and the excess reactant. The limiting reactant is the reactant (of the two/more) that is completely reacted up, or used up, before any other reactant is. When solved for, it is the reactant with the least amount of moles found to be used. The excess reactant is the opposite: It is the reactant that, after the limiting reactant is used up, still has more of that substance left over